This invention relates to an improvement in a differential gear having a differential restricting function.
A differential gear with a differential restricting function allows drive power to be distributed from a power transmitting member to two follower shafts while restricting these follower shafts from being rotated at speeds exceeding a given rotational difference. Such a differential gear is known from, for instance, U.S. Pat. No. 4,509,388 entitled xe2x80x9cDIFFERENTIAL GEARxe2x80x9d.
The differential gear set forth above is comprised of two opposing casing halves and a power transmission member composed of a crown gear disposed between these casing halves. Plural sets of two dish-like cams are disposed in an internal space between the casing halves and the power transmission member to be rotatable with respect to one another. The dish-like cams have follower shafts, respectively. The dish-like cams have an inner cam lobe and an outer cam lobe formed on mutually opposite surfaces of the respective dish-like cams at an area closer to the rotational center and a diametrically outer area, respectively. The inner cam lobe and the outer cam lobes are continuous in a circumferential peripheral direction. The inner cam lobes and the outer cam lobes vary in a radially outward direction. Four small rolling members are disposed between the inner cam lobes, respectively. Likewise, four large rolling members are disposed between the outer cam lobes, respectively. The crown gear supports these rolling members.
When the two shafts meet the same rotational resistance, drive power is distributed from the crown gear to the two shafts via the rolling members and the inner and outer cam lobes.
If one of the shafts meets a larger rotational resistance than that of the other one of the shafts, the rolling members are urged against one of the inner cam lobes and one of the outer cam lobes from the other one of the inner cam lobes and the other one of the outer cam lobes, resulting in a difference in phase in the one of the inner cam lobes and the one of the outer cam lobes. As a result, the two shafts are restricted from rotating at speeds with a rotational difference exceeding a given value.
The differential gear set forth above features that, in order for enhancing a power transmission performance between the crown gear and the two shafts, the cam lobes are radially formed in a doubled structure configuration. More particularly, the opposing outer cam lobes are displaced in phase from the opposing inner cam lobes at an angle of 45 degrees in a circumferentially peripheral direction, with the rolling members of two kinds being aligned in a radial direction and supported with the crown gear.
However, such a structure is apt to be extremely complicated and involves a large number of component parts. Also, a high assembling precision is required. In addition, the presence of the two kinds of rolling members disposed in the radial direction causes the power transmission member, composed of the casing halves and the crown gear, to have no choice but to be inevitably formed in a large diameter. This results in the differential gear with a large sized structure. To address such an issue, it is desired for the differential gear with the differential restricting function to enhance a power-distribution performance between the power transmission member and the two shafts while attaining a miniaturized structure through the use of a simplified construction.
According to the present invention, there is provided a differential gear in which drive power is distributed from a power transmission member to two follower shafts in such a manner as to permit the two follower shafts to rotate with a given rotational difference, the differential gear comprising, the power transmission member rotatable relative to the two follower shafts and internally formed with an inner space, two cam members disposed in the inner space in concentric relation with a rotational center line of the power transmission member to be rotatable with respect to one another and having cam lobes formed on respective opposing surfaces, the follower shafts provided to the two cam members in concentric relation with the rotational center line of the cam members, respectively, and a plurality of cam follower elements interposed between the two cam lobes to be moveable along the cam lobes and to be held in engagement with the power transmission member, wherein each of the two cam lobes is continuous in a circumferential peripheral direction with each cam lobe having a varying height in an axially longitudinal direction of the cam members, characterized in that the power transmission member has a cylindrical inner peripheral surface, defining the inner space, formed with a plurality of engagement grooves lying parallel with the two follower shafts, each of the cam follower elements are fitted to respective one of the engagement grooves so as to cause a longitudinal direction of the each cam follower element to be orientated in a rotational direction, and the cam follower elements have portions, protruding from the engagement grooves into the inner space, which are disposed between two cam lobes.
With such a structure, the differential gear of the present invention is operative to distribute drive power from the power transmission member to the two follower shafts via the cam follower elements and the two cam members even if the cam follower elements assume any positions with respect to the two cam lobes. Especially, since each of the cam follower elements is fitted to each of the engagement grooves of the power transmission member so as to have a longitudinal axis orientated in the rotational direction of the power transmission member, the power transmission member may have a reduced diameter, resulting in a miniaturization of the differential gear.
Each of the cam follower elements, according to the present invention, preferably comprises an elongated member composed of terminal spherical portions and the central constricted portion, or the two balls. The presence of the two balls enables the cam follower element to be formed in a further simplified structure, resulting in a reduction in cost of the differential gear.
Each of the engagement grooves, according to the present invention, has a width shorter than the total length of each of the cam follower elements or the length of the two side-by-side balls. The depth of the groove is preferably determined to have a size substantially half of the diameter of the spherical portion or the ball of each of the cam follower elements. Substantially half of the spherical portion or of the ball sticks out of the inner space side from the associated engagement groove. This sticking out portion is intervened between the two cam lobes.